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Once again ChrisDuggleby.com is among the leaders is reporting a subject which is of global importance (especially if you are a honeybee). Read on to find out about a sophisticated psychoactive chemical reward system that supports a symbiotic relationship between plants and their pollinators (in this case bees).
Last weeks edition of Science (8th March, vol 339) reported on how plants use caffeine in their nectar to help a bee to remember where they can can get another dose of the ‘good stuff’.
We already know that caffeine improves memory in humans. Many of us are certain that our daily caffeine fix helps to improve our clarity of thinking, focus on what we are doing and alertness (or in some cases just staying awake!). Certain high street coffee chains have learnt that by wafting coffee aromas through their doors at passers-by they are able to encourage enthusiastic return visits (and charge their addicts accordingly). However the development of caffeine containing drinks for humans is a relatively recent evolutionary development. As with many biochemicals with interesting properties (like naturally occurring antibiotics) caffeine evolved in plants for a reason. The impact it has on the human brain is merely a by-product of this natural role.
In some plants caffeine in high concentrations acts as a retardant – its bitter taste discourages animals from eating the plants. However at lower concentrations, particularly in nectar the caffeine stops being a retardant and actively encourages visits from pollinating insects. This role of caffeine in nature has been scientifically demonstrated in work done by Geraldine A. Wright et al. in the UK (Geraldine Wright is based at the Centre for Behaviour and Evolution, Institute of Neuroscience, Newcastle University. England and collaborated on this work with an international team including representatives from Newcastle, Dundee, Arizona, the Royal Botanical Gardens at Kew, Greenwich and several ‘volunteer’ honeybees). The article can be found here.
Caffeine occurs naturally in the floral nectar of Coffea and Citrus plants. The research by Wright et al. showed that at the levels occurring in nature the caffeine improved the ability of bees to remember and relocate a floral scent that they have recently ‘learned’. The scientists demonstrated the effect the caffeine had on bee neurones which were associated with the learning of smell recognition and memory. In effect the caffeine enhanced the ability of these neurone systems to learn and remember the smell of the plant where they first experienced the caffeine containing nectar.
In the laboratory honeybees rewarded with caffeine at the concentrations found naturally in the nectar of the Coffea and Citrus plants were, after one day, three times more likely to remember a learned floral scent compared to honeybees which were simply rewarded with a sugar solution (sucrose). Even after three days the bees fed on caffeine were twice as likely to remember the source than their sucrose fed colleagues. Since caffeine at higher dosage levels can repel insects due to its bitter taste, it would appear that the plants have evolved to provide just the right amount of caffeine in their nectar to stimulate the bees’ nervous and learning systems but not enough to repel them.
In this way the plants are utilising caffeine to deploy a classical marketing strategy: they create customer (OK – pollinator) loyalty and encourage repeat purchases (bees who pop in again for a bit more nectar). This helps the plants to be successful in their reproduction and provides the next generation of plants with a successful recipe for attracting their pollinators.
And those high street coffee chains thought they were the first to come up with this customer winning success strategy!
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For german reading visitors to ChrisDuggleby.com an article in the german press about this subject can be found here.